My 1998 XK8 brake pedal seems soft to me. when you push the pedal, it seems spongy not firm like my BMW. brakes work fine but there is also alot of pedal travel as well. Could that be a bad master cylinder?

 

My brothers BMW has a firmer pedal with less travel too, but both my XJS and XKR feel perfectly safe and replacement fluid at service times has never altered the feel!? Passed the UK MOT with no problems.

Has your brake fluid been replaced?

 

Yes, the brakes in my XK8 are softer than my BMW 325. Compared to my Bimmer, the pedal travel is longer; the pads grip slower, and the pedal firmness has a more spongy feeling.

Much of the difference is due to the brake pads. I used the Akebono ceramics in the Jag and while they deposit very little brake dust, they lack the bite of the OEM BMW pads. The OEM BMW pads bite very quickly, but also leave tons of brake dust behind.

Originally, I thought about swapping the OEM rubber lines for some stainless braided lines; however, I could not find anything is stainless lines for the XK8... except of course the R series Brembos, which are completely different calipers.

I ran across a manufacturer of DOT approved braided steel lines who said they would fabricate some if they had an a reasonable market demand. All they need was a complete set to borrow and use as a sample. It might be worth a try to generate interest. I was under the impression they only needed to sell 10 or 12 sets to make it worth their time and effort. They indicated pricing would be market, which is about $200-$250 for a set of four.

 

If it's come on gradually and you haven't changed discs or pad type, then it could be:

1. air in the system
2. brake fluid (deliquescent - picks up moisture over time unless you're using synthetic)
3. master cylinder
4. servo
5. flexi hoses (ballooning as the pedal is pressed from internal wall damage)

A spongy pedal suggests air or the fluid needs changing. A pedal which gradually goes down as you hold the vehicle on the brakes would be more like master cylinder.

When was the fluid last changed?

Graham

 

This has been normal from day one with the car. I have had other cars that a little sponge but the brrakes were fine. EX: Chevy Corvette has a firmer brake pedal than a Lincoln.

I guess it is normal so I won't worry about it unless there is a change for the worse.

Thank you all for your time.